1. Field of the Invention
The present invention relates to a pressure compensating device with a pressure compensating diaphragm for an encapsulated weighing cell for neutralizing an excess pressure or a negative pressure within a protective housing relative to the space surrounding the protective housing.
2. Description of the Related Art
In a balance protected against dust and water known from EP 00 35 579, the measuring system is completely enclosed by a protective housing, wherein the legs of the balance extend through the protective housing and are connected to the latter by means of annular diaphragms which act as sealing means for the protective housing. Moreover, in balances having a small maximum load, means for compensating the pressure differences are provided. These means are porous inserts or bellows which are provided at the bottom side of the protective housing and which are arranged at openings of the protective housing.
However, the arrangement described above has the disadvantage that it does not operate sufficiently effectively in practice. Because of its stiffness resulting from its shape, the bellows is substantially ineffective for the relatively very small and quick pressure differences between the surrounding space and the inner space of the protective housing. This is particularly true when short reaction times of the balance are required, as is the case in industrial applications in which the balance is used within a process apparatus at locations corresponding to the process steps. The embodiment utilizing the porous cover of the pressure compensating opening in the protective housing has the additional disadvantage that it may become at least partially ineffective when the pores are clogged by dust or the like created during the production process and the measuring accuracy decreases as a result. Especially this possibility is particularly dangerous in processes in which the weighing accuracy must meet very high requirements and the weighing accuracy must remain constant over long periods of time.